Anaerobic degradation of benzene, toluene, ethylbenzene, and xylene compounds by Dechloromonas strain RCB

Abstract

Dechloromonas strain RCB has been shown to be capable of anaerobic degradation of benzene coupled to nitrate reduction. As a continuation of these studies, the metabolic versatility and hydrocarbon biodegradative capability of this organism were investigated. The results of these revealed that in addition to nitrate, strain RCB could alternatively degrade benzene both aerobically and anaerobically with perchlorate or chlorate [(per)chlorate] as a suitable electron acceptor. Furthermore, with nitrate as the electron acceptor, strain RCB could also utilize toluene, ethylbenzene, and all three isomers of xylene (ortho-, meta-, and para-) as electron donors. While toluene and ethylbenzene were completely mineralized to CO2, strain RCB did not completely mineralize para-xylene but rather transformed it to some as-yet-unidentified metabolite. Interestingly, with nitrate as the electron acceptor, strain RCB degraded benzene and toluene concurrently when the hydrocarbons were added as a mixture and almost 92 microM total hydrocarbons were oxidized within 15 days. The results of these studies emphasize the unique metabolic versatility of this organism, highlighting its potential applicability to bioremediative technologies.

FIG. 1.

Anaerobic oxidation of [¹⁴C]benzene to ¹⁴CO₂ by strain RCB in the presence and absence of various alternative electron acceptors. The results depicted are the averages of triplicate determinations.

FIG. 2.

Anaerobic growth and benzene oxidation by strain RCB anaerobically with 2 mM chlorate as the electron acceptor. The arrows represent the readdition of benzene. The results depicted are the averages of triplicate determinations. The replicate samples did not deviate from each other by >6%.

FIG. 3.

Aerobic and anaerobic oxidation of ¹⁴C-toluene to ¹⁴CO₂ by strain RCB in the presence and absence of various alternative electron acceptors. The results depicted are the averages of triplicate determinations.

FIG. 4.

Anaerobic ethylbenzene degradation by Dechloromonas strain RCB with nitrate as the sole electron acceptor. The arrows represent refeeds of ethylbenzene. The results depicted are the averages of triplicate determinations. The replicate samples did not deviate from each other by >5%.

FIG. 5.

Anaerobic biotransformation of meta-, ortho-, and para-xylene by Dechloromonas strain RCB. The arrows represent refeeds of the respective xylene isomers. The results depicted are the averages of triplicate determinations. The replicate samples did not deviate from each other by >5%.

FIG. 6.

Cumulative consumption of toluene and benzene by active cells of strain RCB under anaerobic nitrate-reducing conditions when inoculated into medium containing equal amounts of both benzene and toluene. The arrows represent points at which the cultures were refed with the hydrocarbon mixture. The results depicted are the averages of triplicate determinations.